1. Field of the Invention
This invention relates to magnetic bubble domain nucleators, and more particularly to improved nucleators using magnetic walls to assist the nucleation operation. The resulting technique is especially advantageous for use with contiguous elements for propagating magnetic bubble domains, such as the contiguous disk elements typically formed by ion implantation of a magnetic medium.
2. Description of the Prior Art
In the magnetic bubble domain art, bubble domain generators are often employed for producing information bubble domains. Two techniques exist for doing this. In one device, termed a replicator, a seed domain is split to provide new bubble domains. Replicators generally comprise a magnetically soft disk around which the seed domain travels in response to the reorientation of a magnetic field in the plane of the disk. These disk generators operate reliably at quasi-static frequencies but have disadvantages of initialization (i.e., stabilization of the seed bubble) and low phase margin problems at high frequency operation. That is, at high frequencies the control conductor used to assist splitting must be energized at an appropriate time within the cycle of the rotating drive field to reliably replicate the seed bubble domain.
Another type of bubble domain generator is the nucleator, which reverses the direction of magnetization in a localized region of a magnetic bubble domain material. Such a generator does not rely on splitting a seed domain. One example of a typical nucleator is simply a hair-pin conductor loop which when energized with an adequate current pulse nucleates the bubble domain within the loop. Typical current levels required for nucleation of 5 micron bubble domains in a garnet bubble domain material are 400-500 mA. Another example of a magnetic bubble domain nucleator is one where the nucleation field is provided by the stray magnetic field associated with a magnetic element. Examples of both such nucleators are provided in U.S. Pat. No. 3,662,359.
The principles of U.S. Pat. No. 3,662,359 have been utilized in the nucleator of U.S. Pat. No. 3,824,571, which shows the combination of a current carrying line and a magnetically soft element for nucleation of bubbles. The presence of the magnetically soft element provides a magnetic field which aids nucleation, so that the entire nucleation field does not have to be produced by current in the conductor.
In the present invention, a magnetic wall, such as a charged wall, is used to assist nucleation and in fact provides a large percentage of the total nucleation field. The use of a magnetic charged wall means that additional magnetic elements do not have to be provided for part of the nucleator, as is the situation in U.S. Pat. No. 3,824,571. This aids in fabrication, particularly if the additional magnetic elements are discrete elements having small linewidths as is shown in U.S. Pat. No. 3,824,571. Additionally, discrete magnetic elements may not be desirable for certain types of bubble storage devices. In particular, the nucleator of U.S. Pat. No. 3,824,571 is not suitable for use in a bubble storage device utilizing contiguous propagation elements. In such a contiguous element device, ion implanted regions of a magnetic material or continuous sheets of magnetically soft material provide magnetic charged walls which reorient in a plane parallel to the bubble medium. These magnetic charged walls are used for bubble functions, such as propagation. The discrete element structure of U.S. Pat. No. 3,824,571 will not provide these magnetic charged walls and the provision of additional magnetic elements for nucleation would defeat many of the advantages achieved when magnetic charged walls are used in contiguous element bubble devices.
For these contiguous-disk devices, the minimum overlay feature is typically restricted to be no less than about four times the bubble diameter. If a hair-pin conductor nucleator is used with such a contiguous disk device and has that restriction in terms of the minimum overlay feature, this type of nucleator becomes less efficient due to the wide spread of magnetic field produced by the wide nucleating conductor. Additionally, as the bubble size scales downward, the effective anisotropy field (H.sub.K - 4.pi.M), which dictates the minimum current required for nucleation of bubbles, generally scales upward.
The present invention attempts to provide improved bubble domain nucleators, and in particular nucleators which are suitable for use in contiguous propagation element bubble devices utilizing magnetic charged walls.
Accordingly, it is a primary object of the present invention to provide improved magnetic bubble domain nucleation requiring small amounts of nucleating current.
It is another object of the present invention to provide an improved magnetic bubble domain nucleator which is particularly suited for use with bubble devices using contiguous propagation elements.
It is still another object of the present invention to provide an improved bubble domain nucleator which can be used with bubble propagation elements using magnetic charged walls for movement of bubble domains.
It is a further object of the present invention to provide an improved magnetic bubble domain nucleator which can be used with bubble devices designed for storage of very small bubble domains.
It is a still further object of the present invention to provide a bubble domain nucleator of high efficiency, which can be used with bubble devices designed for use with bubble domains of one micron and less in diameter.
It is another object of the present invention to provide a magnetic bubble domain nucleator for use with bubble domain devices having minimum overlay features no less than about four times the bubble diameter.